Two space rocks hours apart â should we be watching the skies more?

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Cape Canaveral, Fla. • A space rock even bigger than the meteor that exploded like an atom bomb over Russia could drop out of the sky unannounced at any time and wreak havoc on a city. And Hollywood to the contrary, there isn't much the world's scientists and generals can do about it.

But some former astronauts want to give the world a fighting chance.

They're hopeful Friday's cosmic coincidence  Earth's close brush with a 150-foot asteroid, hours after the 49-foot meteor struck in Russia  will draw attention to the dangers lurking in outer space and lead to action, such as better detection and tracking of asteroids.

"After today, a lot of people will be paying attention," said Rusty Schweickart, who flew on Apollo 9 in 1969 and helped establish the planet-protecting B612 Foundation. He has been warning NASA for years to put more money into a heightened asteroid alert.

Earth is menaced all the time by meteors, which are chunks of asteroids or comets that enter Earth's atmosphere. But many if not most of them are simply too small to detect from afar with the tools now available to astronomers.

The meteor that shattered over the Ural Mountains was estimated to be 20 times more powerful than the atomic bomb dropped on Hiroshima during World War II, but exploded much higher from the Earth. It blew out thousands of windows and left more than 1,000 people injured in Chelyabinsk, a city of 1 million. And yet no one saw it coming; it was about the size of a bus.

"This is a tiny asteroid," said astronomer Paul Chodas, who works in NASA's Near-Earth Object program in Pasadena, Calif. "It would be very faint and difficult to detect  not impossible, but difficult."

As for the three-times-longer asteroid that hurtled by Earth later in the day Friday, passing closer to the planet than some communications satellites do, astronomers in Spain did not even discover it until a year ago. That would have been too late for pre-emptive action  such as the launch of a deflecting spacecraft if it had been a threat.

Asteroid 2012 DA14, as it is known, passed harmlessly within 17,150 miles of Earth, zooming by at 5 miles per second. Scientists believe there are aywhere from 500,000 to 1 million "near-Earth" asteroids comparable in size to DA14 or bigger out there. But less than 1 percent have actually been spotted.

Earth's atmosphere gets hit with 100 tons of junk every day, most of it the size of sand, and most of it burning up before it reaches the ground, according to NASA. "These fireballs happen about once a day or so, but we just don't see them because many of them fall over the ocean or in remote areas. This one was an exception," NASA's Jim Green, director of planetary science, said of the meteor in Russia.

The chances of Earth getting hit without warning by one of the big ones are "extremely low, so low that it's ridiculous. But the smaller ones are quite different," Schweickart said. He warned: "If we get hit by one of them, it's most likely we wouldn't have known anything about it before it hit."

Bill Cooke, head of the Meteoroid Environments Office at NASA's Marshall Space Flight Center in Huntsville, Ala., said the agency takes asteroid threats seriously. "NASA has recognized that asteroids and meteoroids and orbital debris pose a bigger problem than anybody anticipated decades ago," he said.

Its need cannot be underestimated, Schweickart warned. Scientists will need to know 15, 20 or 30 years in advance of a killer rock's approach to undertake an effective asteroid-deflection campaign, he said, because it would take a long time for the spacecraft to reach the asteroid for a good nudge. "That's why we want to find them now," he said.

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